Today the company announced that free, unlimited video streaming will soon be offered to all its customers. The feature, like T-Mobile’s music streaming promo, promises endless binge-watching for just about every major streaming service — Netflix, HBO, Hulu, ESPN, etc. — with a big exception: YouTube.

It’s a nice deal. But there’s a catch, and it’s a pretty big one. T-Mobile plans to cope with all this extra data by “optimizing video for mobile screens, minimizing data consumption while still delivering DVD or better quality (e.g. 480p or better).”

DVD quality, as companies hawking Blu-ray discs once said, isn’t great. Meanwhile smartphones, for better or worse, continue to grow in size; this trend, combined with the race to pack more pixels into displays, doesn’t pair nicely with degraded streaming, as nice as “unlimited” sounds. And then there’s tethering, which may bring reduced-quality streams to laptops.

A T-Mobile spokesperson kindly addressed my concerns, insisting the feature is a “win-win” for everyone.

Binge On is a win-win as it will optimize video for mobile viewing at 480p, which is approximately 2.2X more efficient than HD coming over the network, with minimal difference in viewing experience. The difference between HD video and 480p is nearly indistinguishable on a mobile device. When Binge On is enabled, T-Mobile customers will be able to watch the same amount of video, while consuming more than 50% less network data than they do while watching in HD.

My eyes aren’t great, T-Mobile, but I find this hard to believe: “The difference between HD video and 480p is nearly indistinguishable on a mobile device.”

Still, it’s a nice feature. And it’s optional. So this is pretty neat. Just make sure you’re comfortable bending the rules of Net Neutrality.

Update 1:28 p.m. PT: Later, T-Mobile declined to share if it set a cap on how high the quality of its streams can go.

T-Mobile’s built new technology into their network to optimize video for mobile screens delivering DVD or better quality. Usually video streams at 480p or better, depending a variety of criteria.

That’s the extent of what T-Mobile is really willing to share at this point.